1. Field of the Invention
The present invention relates to an object information acquiring apparatus and a calibration device.
2. Description of the Related Art
As one of imaging techniques for irradiating light on an object such as a living organism from a light source such as a laser, and converting information concerning the inside of the living organism obtained on the basis of incident light into an image, photoacoustic imaging technique has been proposed. The photoacoustic imaging is a technique for irradiating pulsed light generated from the light source on the living organism, receiving an acoustic wave generated from a biological tissue that has absorbed light propagating and diffusing in the living organism, and subjecting the received acoustic wave to analysis processing to visualize information concerning the inside of the living organism, which is the object.
As the object, a living organism, specifically, a target region of diagnosis such as a breast, a finger, or a limb of a human body or an animal is assumed. A light absorber on the inside of the object relatively has a high absorption coefficient in the object. For example, when a human body is a measurement target, oxygenated or reduced hemoglobin, a blood vessel including a large quantity of the hemoglobin, or a malignant tumor including a large number of newborn blood vessels corresponds to the light absorber. Consequently, it is possible to obtain an optical characteristic distribution in the living organism, in particular, a light absorption coefficient distribution and an oxygen saturation distribution. Researches for diagnosing the object using an image of the light absorption coefficient distribution or the like have been performed.
In a medical diagnostic apparatus such as an X-ray CT apparatus, an MRI apparatus, a nuclear medicine diagnostic apparatus, an ultrasound diagnostic apparatus, or a PET-CT apparatus, a biological tissue model called human body tissue stimulant material (phantom) is used in order to perform performance evaluation and calibration in a scene such as inspection of the apparatus. As a material of the phantom, a material close to characteristics of the human body tissue and a material that can be stored for a long period without causing, for example, proliferation of unwanted bacteria are demanded. The phantom is set in the medical diagnostic apparatus and scanned to collect data. Then, performance evaluation is performed from the collected data and a calibration place and a calibration amount are searched.
The phantom is manually set in an image pickup setting region when the performance evaluation or calibration of the medical diagnostic apparatus is performed. Therefore, a position and a tilt for setting the phantom are different every time. Therefore, positional deviation or the like of a captured image occurs and accuracy of a measured image cannot be guaranteed. It is also attempted to affix a mark to an image pickup region with a tape or the like and place the phantom in a fixed position as much as possible. However, since a setting person only sets the phantom according to his or her senses while visually checking the mark, it is difficult to strictly manage the setting of the phantom. Therefore, as a method of accurately setting the phantom, there is proposed a positioning method for fixing a positioning frame size using a plurality of pins in a calibration device for the phantom (Japanese Patent Application Laid-Open No. 2009-101193).
Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-101193